Research seminar Sophie Vanvooren - 8 January 2014

Technical Comparison Sennheiser HDA 200/300

In our lab, the Sennheiser HDA 200 headphones are widely used for anything audiology related. They are pleasant to wear for a long time, have a flat frequency response and high passive ambient noise attenuation as they are based on PELTOR hearing protectors.

Sadly, these headphones went out of production. And according to Sennheiser, there is no way that they will resume production. Instead, they recommended their designated successor headphones, the Sennheiser HDA 300.

Official technical information

For both headphones, technical data sheets with information on passive attenuation and sensitivity level (frequency response) are available from the Sennheiser website (HDA 200, HDA 300).

For passive attenuation above 250 Hz, the HDA 300 is worse than the HDA 200, with an average difference of 16 dB for the frequencies range from 500 Hz to 8 kHz.

For the flatness of the sensitivity level, the profile of the HDA 300 has a standard deviation of 9 dB (octave frequencies 125 Hz to 16 kHz), which is nearly twice as much as the 5 dB for the HDA 200.

The HDA 300 headphones weight 490 g, an increase of 50 % over the 330 g of the HDA 200. The transducer impedance of 40 Ohm is reduced to 23 Ohm.

Own measurements

We tried to reproduce the data on passive attenuation and sensitivity level for the two types of headphones. The measurements were done in a sound-proof room with a Brüel & Kjær artificial ear 4153, with 4 speakers creating a diffuse noise sound field of about 70 dB(SPL). For the frequency sensitivity measurements, a continuous sweep was used. One side of the headphones was placed on the artificial ear, while the other side was wrapped around a side of the measurement table.

With this setup, we could observe a smaller difference in passive attenuation of 8 dB (octave frequencies 2 to 8 kHz) for frequencies above 2 kHz instead of 500 Hz. For lower frequencies, no difference was found. We suspect that the difference between our measurements and the official Sennheiser data is caused by our less-than-perfect measurement setup, especially the way we fixed the headphone to the artificial ear.

For the sensitivity level, we measured a standard deviation of 3 dB for the HDA 200 and 9 dB for the HDA 300 (octave frequencies 125 Hz to 16 kHz).

tl;dr (Summary)

Compared to the HDA 200, the HDA 300 headphones have less passive attenuation, a worse frequency sensitivity profile and are much heavier. We are not impressed.

Holyhour Bernhard Laback Tuesday 17 December 2013

Holyhour Christian Lorenzi Friday 13 December 2013

Hearing without Hearing.

By Christian LORENZI, Ecole normale supérieure, Paris, France.

The audiogram reflects the limits of the auditory system's  ability to encode acoustic information  in a soundwave. It is measured typically as the detection threshold for a pure tone (a sinusoid) as a function of sinusoid frequency.  The audiogram provides an indication of how well variations in sound pressure are preserved by the auditory system. However, it does not inform about the fidelity of sound encoding. The question of encoding fidelity is crucial because it indicates “the extent to which variations in the strength of a given supra-threshold auditory feature can convey information about the acoustic signal. A limiting case  of encoding  fidelity is that in which sounds are well detected, but no further  information  about the changes in the sounds parameters is  preserved;  in this case, the encoding fidelity is poor” (Wakefield & Viemeister, 1990). Here, we will review psychophysical evidence that such a “limiting case of encoding fidelity” may be frequently observed for patients with sensorineural hearing loss. In other words, we will show that abnormal encoding fidelity may arise despite normal auditory sensitivity for patients with sensorineural hearing loss. This will be demonstrated for several speech identification tasks performed in the low- or mid-frequency regions where patients with high-frequency sensorineural hearing loss show normal or near-normal auditory sensitivity (Léger et al., 2012a,b,c; Bruce et al., 2013; Stasiak et al., 2013; Goodman et al., 2013). Taken together, these results: (i) confirm that normal auditory sensitivity (as measured clinically by the audiogram) is not sufficient to guarantee robust encoding of certain spectral and temporal suprathreshold auditory features critical in daily listening situations, and (ii) raise the need for using discrimination/identification tasks in auditory screening.